euscanwww: move processing to scan and misc, enhance update_portage_tree

update_portage_tree() now:
- watch stderr and stdout for each command
- use layman command instead of layman API for sync because
  layman API doesn't work when stdout or stderr is not a real file
  (we could probably work around that with pipes and epoll)
- use egencache instead of emerge to generate cache
- export PORTAGE_CONFIGROOT, ROOT, EIX_CACHEFILE etc.. so they
  are used everywhere

Signed-off-by: Corentin Chary <corentin.chary@gmail.com>

euscanwww/djeuscan/management/commands/regen_rrds.py

@@ -2,11 +2,10 @@ import logging
 from django.core.management.base import BaseCommand
 
 from djeuscan.processing import set_verbosity_level
-from djeuscan.processing.regen_rrds import regen_rrds
+from djeuscan.processing.misc import regen_rrds
 
 logger = logging.getLogger(__name__)
 
-
 class Command(BaseCommand):
     _overlays = {}
     help = 'Regenerate rrd database'